You’ve said phoenix is approximately 70 percent (I think) the size of Firefly. Looking at the artifacts I did the math on the hole carriers and the spring hole on the elenovo find is more like 85% the size of the orsova. I thought that dimension was the starting point for the craftsmen to get all the other measurements. Do you think they started to change that part of the formula for beefed up lightning ballistae? I hope someone stumbles upon a couple more of these machines. Not holding my breath.

P.S. I didn’t know that behemoth discovery channel ballista only got 120 yards! You say it was built by authorities in the field of ancient artillery study? My gosh how embarrassing. I’d have used a D9 CAT to stretch with myself. They should pay us to build something. All that money, beautiful beautiful, money to use.

And here is my reply:

.729 is the number I’ve been using. You are correct that the spring diameter is the primary reference dimension that ancient craftsmen were supposed to use to scale their machines when being guided by the ancient formulas. However, because this is an artifact based reconstruction, I figure that the overall height of the field frames should be taken into account when scaling the machine. Others will no doubt disagree, but to my way of thinking this gives us a more accurate starting point for figuring the length of the kamarion and the consequent distance between the springs. Let’s face it, in the modern age, this is all pretty much guess or by golly. Close enough for horseshoes and hand grenades etc. The formula folks will sputter I’m sure, but as far as I’m aware, none of them have actually made a truly powerful machine yet.

And re: John’s P.S. :

Yeah, it does seem a shame that all that lolly produced so much feeble. The fact that the BBC machine, designed by Wilkins & co., does not have any metal plating to reinforce all that beautiful woodwork, was a clear indication that this machine would be under-stressed and therefore a bit of a wimp.

Photo courtesy of carpenteroakwoodland.com

This is what happens when woodworkers take charge of torsion engine design. In my experience with conventional “wood” machines, it takes lots of iron as well as wood to make a powerful ballista. And also a willingness to exploit high levels of torsion to match all that frame strength you created by using the iron reinforcement.

The two photos above are of my first machine, dubbed the “Gallwey”, after his Lordship, Sir Ralph Payne Gallwey. Almost certainly, no ancient ballista ever looked like this piece. Note, however, the use of iron plates on the inside of the boxframe and the through bolting to the plates on the outside. This was a powerful outswinger with 1150 foot pounds of muzzle energy and a 750 yard maximum range. You can hear what that kind of power sounds like in this ridiculously grainy video. Click for vid: gallwey-1a What you are seeing is a 1″ blunt bolt zipping through a target made of four sheets of 3/4″ plywood. (For more on this Victorian knock-off, see archives, The Gallwey Carroballista, Dec 16, 2008.)

The point is, without all that metal plating ……. well, forgetaboutit. We’d have been lucky to get through the first sheet because the torque would have needed to be set so low for the machine to survive.

There are several passages in the artillery manual of Heron where the importance of metal plating on the wood framework is emphasized. In Marsden, Heron says on page 29, “You must see that the grain of the wood runs up and down the side stanchion and covers its sides on either hand with plates binding them with nails.” Or later, on page 35, “You must also provide iron plates at critical points, I mean points that must withstand hard usage, and fasten them on with nails.”

While it is true that Heron was probably a few hundred years later than the machine represented by the BBC analog, the indirect lesson from the old master is that real torsion engines are meant to be run at wood shattering levels of torque. His assessment that metal reinforcement was essential would have been as true for the Ancient Greeks as it was for the Romans. Wood is wood, no matter how fine the joinery.

It seems that the team that built the BBC machine took on the most difficult of catapult reconstructions. Apparently one that forbade the use of metal plating, a stricture that is perhaps not as authentic as many purists seem to believe. Probably they only had the ancient directions for all that fab looking joinery; the addendum, “and then reinforce with metal plates”, somehow went missing.*

Interestingly, we see plenty of iron plating on various pieces of original framework that have been uncovered. The Hatra is a good example of this. Or how about this photo of the Emporium ballista, all decked out in iron.

Photo filched from Samuli’s, Greek and Roman Artillery Wiki. (Note the handful of glandes in this museum display. Surely the curator is not so avant-garde as to suggest that these missiles would be suitable fodder for a ballista?)

“Building the impossible” — as a professional metal worker that has his doubts about an overreliance on timber in high shock applications, I always thought the BBC attempt aptly named.

*In contrast to his BBC machine, is Proffesor Wilkins use of metal plating on the Xanten-Wardt reconstruction made by those master modelmakers, Mr. Morgan and Mr. Feeley. I particularly admire this rendition because it is an artifact based reconstruction. A truly beautiful and authentic reconstruction in every respect. … Well, other that is, than any indication of it’s performance specs. At least, as far as I can find.

I wonder, are there laws in the UK that limit the power of torsion catapults? I know that airguns have a power restriction on them over there. It just seems strange that such an obviously deep piece of work has no test results available.